788. Rotated Digits

X is a good number if after rotating each digit individually by 180 degrees, we get a valid number that is different from X.  Each digit must be rotated - we cannot choose to leave it alone.

A number is valid if each digit remains a digit after rotation. 0, 1, and 8 rotate to themselves; 2 and 5 rotate to each other; 6 and 9 rotate to each other, and the rest of the numbers do not rotate to any other number and become invalid.

Now given a positive number N, how many numbers X from 1 to N are good?

Example:
Input: 10
Output: 4
Explanation: 
There are four good numbers in the range [1, 10] : 2, 5, 6, 9.
Note that 1 and 10 are not good numbers, since they remain unchanged after rotating.

Note:

• N  will be in range [1, 10000].

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解题思路：输入N,判断数字是否是good数字。旋转180度变成另一个数，2 5 6 9旋转后是good数字。0 1 8旋转后是本身

含有3 4 7的不是good数字

class Solution {
public:
    int rotatedDigits(int N) {
        int count=0;
        for(int i=1;i<=N;i++){
            
                if(judge(i)){
                count++;
            }
            
        }
        return count;
    }
    bool judge(int N){
        bool flag=false;
        while(!(N%10==0&&N/10==0)){
            int k=N%10;
            if(k==3||k==4||k==7){
                flag=false;
                break;
            }
            if(k==2||k==5||k==6||k==9){
                flag=true;
            }
            N/=10;
        }
       
        return flag;
    }
};